Small electrically-operated valve assemblies, commonly referred to as solenoid valves, are widely utilized for purposes of controlling systems or other components, such as main flow-control valves, small pneumatic cylinders, etc. These solenoid valves are utilized extensively in pneumatic control systems, and conventionally are of the three-way type in that they are provided with supply and exhaust ports and additionally have a load port so that pressurized air can be utilized for controlling a primary system component such as a main flow-control valve. These solenoid valves, being utilized for control of small volumes of air, hence are of small size and every effort is made to minimize the size and maximize the efficiency of the solenoid so as to reduce the power requirements thereof. Additionally, reduced power requirements permit cost and size reductions of electrical control components. However, even though these solenoid valves are extensively utilized and many different variations thereof are manufactured and sold by many different manufacturers, nevertheless these known solenoid valves have still possessed structural and operational features which have been less than desired, and hence have created disadvantages relative to use of such valves, which disadvantages have nevertheless been tolerated and accepted in view of the inability of the industry to satisfactorily improve on these valves.
This conventional solenoid valve typically employs an elongated movable plunger disposed within and surrounded by a solenoid coil, the plunger being activated by the solenoid coil in opposition to the force of a spring. The plunger typically has a recess in the end thereof in which is positioned a pluglike sealing member, which sealing member is substantially constrained by its mounting within the plunger but has an exposed end face which is adapted to create a sealing engagement with an opposed seating surface disposed in surrounding relationship to a fluid supply orifice. This latter orifice communicates with the supply port for the pressure fluid and is normally formed either directly in a housing plate, or in a separate orifice member which is fixedly secured to the orifice plate. The orifice, at its discharge end, is surrounded by the seating surface, the latter typically being a metal surface which is of a convex conical configuration. This typical solenoid valve, while extensively utilized, has nevertheless possessed structural and operational features which have been considered less than optimum but have nevertheless been accepted in the absence of better alternative valves.
One of the disadvantages with this known solenoid valve is its electrical energy consumption, and hence the heat generated during valve operation. This type solenoid valve typically employs a plunger stroke of about 1-32nd inch. This stroke requirement hence increases the power requirement of the solenoid in order to effect movement of the plunger, which power requirement is further increased by the fact that the return force on the plunger as effected by the return spring proportionately increases in response to this increase in stroke. The electrical energy required for operating this typical solenoid valve has hence been an undesirable, yet accepted, operational feature.
A second disadvantage of the typical solenoid valve is that the accumulation of conventional manufacturing tolerances of the individual parts, when the valve is assembled, greatly effects the desired spacing between the plunger and the orifice seat. In fact, maintaining this spacing of small magnitude has been substantially impossible inasmuch as the accumulated tolerances often exceed the desired stroke. For this reason, many manufacturers have utilized an assembly technique which essentially requires preassembly of each individual solenoid valve so as to permit precise measurement of the actual gap or stroke between the plunger and the orifice seat, following which the valve is again disassembled and suitable adjustments made, such as installation of shims, so as to result in a stroke or gap within acceptable tolerances. Needless to say, this type of production procedure is extremely time consuming and costly. Also, many of the valves provide the conical orifice seat directly on a lower plate which forms a part of the valve housing, or in the alternative provide this conical orifice seat on a separate metal orifice member which must be press fitted or otherwise secured to a housing plate, and this obviously requires a time consuming and expensive machining operation in order to provide such conical orifice seat.
A third and very significant disadvantage of this typical solenoid valve is the substantial wear of the seal member which in most instances is mounted and confined within a recess formed in the end of the plunger. It has been observed that this seal member wears at a rate which greatly reduces the overall operational life of the valve in terms of the number of valve cycles which can be performed, prior to rebuilding of the valve and replacement of the seal member. Further, this excessive wear of the seal member also has an effect on the valve stroke, in that it tends to increase the required valve stroke to effect successful sealing, and increases the initial power requirements. Because of this, the power (and possibly also the allowable stroke) is normally increased significantly during the initial design of the valve in an attempt to compensate for the anticipated wear of the seal member. While the exact reasons for the more rapid wear of the seal member is not fully understood, nevertheless it is now believed that this accelerated wear is due to the fact that the elastomeric material of the seal member is repetitively subjected to compression whenever the plunger engages the conical seat so as to close off the orifice, and inasmuch as the seal member itself is closely confined within the plunger, the elastomeric material hence is subjected to substantial compression and cannot freely deform or expand outwardly away from the conical seat due to the substantial penetration of the latter into the central part of the seal member.
Still a fourth disadvantage of many typical solenoid valves is the increased wear experienced when the valve is mounted in a horizontal orientation. This typical valve normally provides excessive clearance between the plunger and the surrounding housing, which clearance permits the air to escape from the load port upwardly past the plunger through an exhaust port located adjacent the other end of the plunger. This excessive clearance, when the valve is mounted horizontally, causes substantial misalignment of the plunger and hence excessive wear thereon.
Accordingly, this invention relates to an improved plunger-type solenoid valve which is believed to overcome the above disadvantages. More specifically, the improved solenoid valve of this invention permits the stroke to be greatly minimized and rather precisely controlled so that the electrical energy required for valve actuation, and the related heat generation, are hence greatly minimized. This improved solenoid valve also minimizes and in some cases eliminates costly machining operations so that the valve can also be manufactured more efficiently and economically. This improved solenoid valve also provides an improved seal arrangement coacting between the plunger and the orifice, which in conjunction with the reduced stroke, greatly minimizes seal wear and hence greatly increases the operational life of the valve, while at the same time also permitting the valve to be manufactured and assembled with increased efficiency.
In the improved solenoid valve of this invention, there is provided a housing having an elongated plunger slidably supported therein, which plunger is surrounded by a solenoid winding. The plunger, at one end, terminates in an enlarged head disposed within an interior chamber, and a spring confined within this chamber reacts between the housing and the plunger head for urging the plunger into engagement with a conical seat which is formed on an orifice member for sealingly closing the orifice which extends therethrough. The orifice member is of a tubular construction and is of an elastomeric material, and is seated within the supply port so that the end portion of the orifice member, which end portion is conical and defines the conical seat thereon, projects into the interior chamber and is free of surrounding restraint. The opposed plunger head defines a metal seal face thereon in opposed relationship to the orifice member so that when the valve is closed, the rigid seal face on the plunger engages the conical end portion of the elastomeric orifice member, which causes limited deformation of the orifice member so as to sealingly close the orifice. The seal face on the plunger head contacts the orifice member so that the latter can freely expand radially outwardly in an unrestrained manner so as to minimize compressive deterioration of the orifice member while achieving a desired sealed engagement. The elastomeric orifice member is inserted into the supply port through the outer end thereof, which insertion occurs after the remainder of the valve has been assembled. The orifice member can be positioned so as to precisely control the gap between the plunger head and the orifice member, which gap (and hence plunger stroke) can be controlled so as to be in the range of 0.010 and 0.013 inch, thereby minimizing the energy requirements of the solenoid coil. The orifice member is compressively seated and stationarily held on the wall of the supply port so as to effect peripheral compressive and sealing engagement with the orifice member, whereby the provision of shoulders or other devices for axially restraining the orifice member is not required. The housing, and more specifically the coil spool, defines an opening therethrough which slidably guides the plunger by means of a close sliding fit. The spool is formed with a plurality of circumferentially spaced but axially elongated ribs so as to provide close slidable confinement of the plunger while resulting in minimum frictional engagement. At the same time, the grooves defined between the ribs function as passages for permitting exhaust air to flow past the plunger and through an exhaust port located adjacent the other end thereof. This latter exhaust port also has an elastomeric orifice member compressibly seated therein, which orifice member also terminates in a deformable conical nose portion which projects toward and is sealingly engageable with an enlarged rigid planar seal face formed on the opposed end of the plunger.
In the improved solenoid valve of this invention, the stroke can be maintained at a minimal amount, such as between 0.010 and 0.013 inch, in contrast to prior valves of this general type which have normally required a stroke of approximately 0.030. At the same time, this improved solenoid valve can be operated with approximately one-half watt of energy, whereas prior valves of comparable specifications have possessed higher energy requirements and have typically required an average of one to four watts for proper performance. In addition, initial testing of the improved solenoid valve of this invention indicates that, with this improved design and with utilization of the elastomeric orifice member, the valve has exhibited a useful life, as measured in terms of operational cycles, which is several times greater than the useful life of known solenoid valves. The elastomeric orifice member also enables the solenoid valve of this invention to be substantially fully assembled in its entirety prior to mounting of the orifice member, following which the orifice member can be inserted into the supply port from the outer end thereof to permit precise positioning thereof so as to maintain the desired stroke within very narrow limits, with the elastomeric orifice member being stationarily and sealingly seated on the valve housing due to elastic compression thereof.
In this solenoid valve, the supply port is preferably provided with an axially elongated cylindrical wall portion which surrounds the nose or orifice end of the orifice member and also surrounds a majority of the axial length of the orifice member. This wall portion is normally slightly oversized in relationship to the normal orifice member diameter so as to provide a small clearance therebetween, but this wall portion is also provided with an axially ribbed or knurled structure thereon, which ribs are circumferentially narrow and extend axially along the wall portion and project radially inwardly so that the plurality of ribs define an inner diameter which is smaller than the orifice member diameter. This plurality of circumferentially spaced ribs hence create localized compression and hence an interference fit with the orifice member in such manner as to stationarily and fixedly seat the orifice member within the supply port, while at the same time this compression of the orifice member by the circumferentially spaced ribs is such as to avoid distortion of the orifice or of the conical seat defined on the projecting end of the orifice member. A suitable adhesive is also preferably applied between the surrounding wall and the periphery of the orifice member which, in conjunction with the axially elongated ribs, greatly facilitates the insertion of the orifice member into the supply port without causing disruptive distortion of the orifice member, while at the same time enabling the orifice member to be properly stationarily seated. The adhesive effectively sealingly engages the orifice member to the surrounding wall.
Yet another improvement in this solenoid valve relates to the structure of the plunger and its cooperation with the orifice member for sealingly closing off the orifice. The plunger as disposed opposite the orifice member is preferably provided with a projection thereon, such as a semispherical projection, the latter being preferably provided by means of a ball fixedly seated within a shallow recess formed in the end of the plunger. This projection or ball has a diameter which is slightly larger than the orifice diameter, such as preferably about 1.5 times the orifice diameter, so that the ball will hence seat against the rounded edge which surrounds the outer end of the orifice. The spherical configuration of the ball permits it to effectively self-align and hence sealingly close off the orifice, even when the plunger is slightly misaligned. The projection or ball must be sized so as to create this self-aligning and sealing relationship with the orifice member, and thus must be slightly larger than the orifice diameter, but cannot be of greatly larger diameter since this would greatly minimize or restrict the desirable self-aligning and sealing relationship. However, the ball is sized so that it does not cause any substantial penetration of the orifice, and hence does not reduce the anticipated long life of the orifice member.
In this improved solenoid valve, the plunger is preferably provided with a radially enlarged platelike head which is positioned axially adjacent and in radially overlapping relationship with a frame plate of the solenoid so as to maximize the magnetic field, and hence minimize power requirements.
This improved solenoid valve also has an improved manual override associated therewith, which override employs an elastomeric ball coacting between the plunger head and the manually rotatable cam. This improved override enables the cam to be rotated a complete revolution, whereas the deformable ball compensates for dimensional variations which might otherwise interfere with cam rotation.
Other objects and purposes of the invention will be apparent to persons familiar with valves of this general type upon reading the following specification and inspecting the accompanying drawings.